This invention relates to lithographic duplicating and especially to the control of moisture application to the master during printing.
The problem of moisture control has been a persistent one, and many different types of moisture application systems have been developed with varying degrees of success. One fairly standard construction employs molleton covered rolls which are moisture absorptive and provide a reservoir situation which proves rather effective under the control of a trained operator, but in the hands of untrained people can be difficult to manage. For example, a slightly low moisture setting will eventually cause the molletons to dry out and ultimately ink up which requires a complex molleton changing procedure, and excessively high moisture setting, on the other hand, will eventually cause the molletons to become over-wet and necessitates delaying printing operations until they can be dried out sufficiently to proceed. In addition, of course, molleton covers present the familiar built-in problems of lint production and a tendency to irregularity of the roll surface.
A number of moisture systems which are free of molleton coverings (and of the attendant reservoir effects) have been developed, and while they escape the above-mentioned drawbacks, they are still significantly reliant upon trained operator control because of their sensitivity. That is to say, very slight changes in adjustment, or changes in moisture demand the master environmental conditions of humidity, run length, ink temperature or condition due to previous running or non-running, can cause the moisture situation to shift quickly either to a low moisture or to an over-wet condition with the result that copies are damaged and time can be lost in restabilizing the system, unless a skilled alert operator is available to prevent the condition from maturing unduly, or to reestablish correct operating conditions quickly once the aberration is recognized.